In many integrated circuit designs, it is necessary to have local reference voltages of known values that are stable among process and temperature variations. With advances in semiconductor technology, the semiconductor geometries are decreasing. In particular, with the scaling of semiconductor technologies and the use of ultra-thin gate oxides, the demand for low power and low voltage reference circuits is increasing strongly. A well-known technique for providing a regulated reference voltage is the band gap reference circuit, which may be utilized as a general-purpose voltage regulator circuit for supplying a stable voltage reference in, for example, an integrated circuit. However, a drawback of the traditional band gap reference circuit is that it uses an arrangement of semiconductor diodes that are unable to operate at power supply voltages less than about 1.0 volts, because the forward bias of a diode is around 0.7 volts and, thus, the proper voltage margins may not be maintained. Consequently, as semiconductor technologies advance and the operating voltages decrease, traditional band gap reference techniques have reached the limit of their voltage margins.
For these reasons, a need exists for a voltage reference circuit for use in low voltage applications in an integrated circuit, in order to replace diode-style band gap reference circuits that are unable to operate with power supply voltages that are less than about 1 volt.